1. Field of Technology
The present invention relates to a commutation type DC breaker and more particularly to a structure of a commutation type DC breaker for supplying charges stored in a commutation capacitor to a main switch in an opposite direction to a main circuit current, producing a current zero point, thereby breaking the main switch.
2. Description of Related Art
FIG. 3 is a drawing for explaining the breaking principle of the commutation type DC breaker. As shown in FIG. 3, a commutation type DC breaker 18 or 19 is connected between a direct current source 60 and a load 70 and includes a main switch 3 with the main circuit current supplied, a supersaturation reactor 10, a commutation circuit composed of a commutation capacitor 8 and a commutation switch 2, a charging power source, not drawn, for the commutation capacitor, and a control unit for controlling the aforementioned units. Further, the commutation type DC breaker 19 is connected to an external circuit, the commutation capacitor, and the supersatuation reactor via contactors 14A, 14B, and 14C.
When an excessive current is supplied to the main circuit 17A, the commutation type DC breaker 19 releases the main switch 3 and simultaneously turns on the commutation switch 2. At this time, the charges stored in the commutation capacitor 8 are discharged via the main switch 3 and a high frequency discharge current (a commutation current) accompanying discharge of the capacitor is supplied to the main switch 3. If the commutation current is superimposed on the main circuit current in this way, a current zero point is generated in the main circuit current and then the main circuit current is cut off (refer to Patent Documents 1 and 2).
FIG. 4 is a cross sectional view showing an example of the conventional commutation type DC breaker 19 arranged in a power board. In FIG. 4, a numeral 40 indicates a power board and it includes a front storage box 40A, a DC breaker storage box 41, and a back storage box 42A. In the front storage box 40A, a power board control unit 30A, terminal boards 20A, 20B and 20C, and a front door 31 are arranged. In the DC breaker storage box 41, the commutation type DC breaker 19 is arranged.
The commutation type DC breaker 19 includes the main switch 3, a main switch drive unit 1 for driving the main switch, main switch control circuits 4 to 7 for controlling the main switch drive unit, the commutation switch 2, the commutation capacitor 8, the supersaturation reactor, and a non-linear resistor 9 which are units necessary for commutation, and these units are arranged in the DC breaker storage box 41. On the back of the main switch 3, a main circuit conductor 17 is arranged. The main circuit conductor 17 is connected to a bus 13 via the main switch 3. A numeral 11 indicates an overcurrent detector mounted on the main circuit conductor. In the back storage box 42A, a cable 44 connected to an external load (a feeder) is stored. The cable is connected to the main circuit conductor 17 via a connecting conductor 21. Further, on the cable connecting conductor 21, a meter DC transformer 26, a DC transformer 23A, and a feeder failure selection unit 22 are mounted.
As shown in FIG. 4, the conventional commutation type DC breaker 19 includes the main switch 3, commutation switch 2, commutation capacitor 8, supersaturation reactor 10, and non-linear resistor 9 and for example, the commutation capacitor 8 and non-linear resistor 9 are arranged in the power board 40 in the vicinity of the main switch 3.    Patent Document 1: Japanese Patent Laid-open No. 2000-48686    Patent Document 2: Japanese Patent Laid-open No. 2001-143581